The grasp reflex consists of progressive forced closure of the hand (contraction of flexor and adductor muscles) when tactile stimulation (e.g., the examiner’s hand) is moved slowly, exerting pressure, across the patient’s palm in an upward direction. Once established, the patient is unable to release the grip (forced grasping), allowing the examiner to draw the arm away from the patient’s body. There may also be accompanying groping movements of the hand, once touched, in search of the examiner’s hand or clothing (forced groping, magnetic movement). Although categorized a reflex, it may sometimes be accessible to modification by will (so-called alien grasp reflex). It is usually bilateral, even with unilateral pathology. Foot grasping (i.e., flexion and adduction of the toes and curling of the sole in response to pressure on the sole), may coexist, as may other Frontal Release Signs (e.g., pout reflex, palmomental reflex, gegenhalten).
The grasp reflex may be categorized as a frontal release sign (or primitive reflex) of prehensile type, since it is most commonly associated with lesion(s) in the frontal lobes or deep nuclei and subcortical white matter. Clinicoradiological correlations suggest the cingulate gyrus is the structure most commonly involved, followed by the supplementary motor area.
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Schott JM, Rossor MN. The grasp and other primitive reflexes. Journal of Neurology, Neurosurgery and Psychiatry 2003; 74: 558-560